Losing sense of smell disrupts digestion

DW: What did you find out when you looked at these roundworms?

Fabian Finger: We found that the sense of smell has a strong impact on the functionality of the gut.

So If I smell food, my body starts to get prepared not just for food generally, but for that specific kind of food?

Yes. 

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If I smell a hamburger, then my body's thinking, "OK, get ready to process a hamburger?"

That goes a bit too far. But there are clear differences in terms of what kind of food source you're smelling.

What did the roundworms smell, and how did their bodies react? 

They usually eat bacteria. So what they smell is living bacteria. And depending on what kind of bacteria you give them to eat, the worms react differently, based on the smell.

So "Bacteria A" smells one way, "Bacteria B" smells the other way, and the worm's body is getting ready to digest one of them, based on smell.

This is what we assume. What we see is there is a clear difference depending on what kind of bacteria the worm smells. 

How did you look inside them?

Our main readout is this "glowing wastebag" phenotype. So whenever the worm is green, it has a problem with its recycling system.

How does smell impact that?

When you disrupt parts of the sense of smell, you see an accumulation of these "wastebags" — a bright green glowing worm, literally, which tells you that the recycling process is severely limited. 

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So if I'm the worm and I can't smell, I'm going to have more waste sitting in my gut, not being productively used. Is that a fair way to put it?

It's a bit more complex. What we assume is that the sense of smell is not reacting properly. It's inhibited in a way — you can measure that — but the information that's being processed from the neurons is, well, not correctly integrated into the system. And it sends a signal that is not suitable for the situation. 

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We've been talking about roundworms, but you work in a department that deals with aging. I know Alzheimer's and dementia patients often have an issue with their sense of smell. Is there something practical we can learn here for humans?

Of course I need to be careful, because I'm looking at roundworms. However, the roundworm is constantly used as a model for neurodegenerative diseases. And as you said, you see the loss of smell early on in the phase of those diseases. It's widely considered to be a consequence of the disease rather than the cause.

So if I have an issue with my sense of smell, that would impact how I digest foods.

In theory. That would be the hypothesis. 

Fabian Finger is a researcher in Cologne, Germany at the CECAD center, or Cellular Stress Responses in Aging-Associated Diseases. He's the lead author of a new report published in Nature Metabolism entitled, "Olfaction regulates organismal proteostasis and longevity via microRNA-dependent signalling."